A common multi-tier automatic warehouse includes a stacker crane and two blocks of multi-tier racks disposed on both sides of a track along which the stacker crane travels. Each tier supports a number of loads on their pallets. For unloading a load on its pallet from the rack, the stacker crane is anchored on the track and its carriage is elevated to the rack. Then, a fork-lift apparatus on the carriage is actuated to extend its forks under the pallet. When the carriage is further elevated, the forks lift up the pallet with the load. The fork-lift apparatus is then actuated to retract the forks allowing the load on the pallet to be loaded on the carriage. After the carriage is lowered by a lifting mechanism, the stacker crane travels to unload the load.
In case that the load is of a roll form having a given outer diameter and a center aperture arranged in discrete location and size, it may not appropriately be loaded and unloaded with the use of such a conventional fork-lift apparatus in a multi-tier automatic warehouse. For smooth handling of loads, any improved fork-lift apparatus is desired. In addition, the stacker crane equipped with a conventional fork-lift apparatus is relatively large in width at the carriage and its track occupies a considerable space in the multi-tier automatic warehouse.
If a rolled good is strapped on a pallet for ease of storage (or handling) in a multi-pier automatic warehouse, its overall size including a pallet height and a fork accepting clearance is increased and requires the tiers or racks to be vertically arranged at intervals of a wider distance. This will impair the optimum use of a given interior space of the warehouse. Also, the time required for handling is increased as each rolled good has to be preliminarily strapped on its pallet, thus contributing to the rise of the working cost.
When the rolled goods are identical in the size, their center apertures into which a fork of the stacker crane is inserted are located in the same place. Accordingly, the goods may be loaded and unloaded with a conventional fork-life apparatus by repeating the same fork inserting action.
In most cases, the rolled goods are different in the location of the center aperture and stored in discrete places in the warehouse. Hence, when one of the rolled goods is required for unloading, its center aperture is viewed and identified by the operator of the stacker crane so that it can accept the fork successfully.
When the load to be handled is of a cylindrical shape having a center bore for accepting the fork of a fork-lift apparatus, it is also viewed and identified by the operator for insertion of the fork into the center bore as it is different in the size and location of the center bore from other loads stored in the warehouse.
It is thus necessary for the operator of a conventional fork-lift apparatus to view and identify the size and location of a center aperture of a desired load to be handled and manually control the fork for insertion into the center aperture of the load. This action will not contribute to the reduction of the working time during the handing of load for storage but impairing the working efficiency.
In particular, even if the center aperture of a load into which the fork of the fork-lift apparatus is inserted has been recognized at the loading to a storage space, it has to be examined again at the unloading from the same.
Also, the manual control of the fork movement by viewing may depend on skills and conditions of the operator. It is probable that excessive brightness or illusion causes the operator to lose the visual estimation of a correct distance resulting in collision of the fork against and damage to the load.
It is an object of the present invention, in view of the foregoing aspects, to provide a fork-lift apparatus in a stacker crane capable of loading and unloading loads of a rolled form smoothly on the racks or tiers of a multi-tier automatic warehouse while the width of a track on which the stacker crane travels is minimized thus contributing to the reduction of each unit storage space in the multi-tier automatic warehouse without sacrificing the storage amount.
It is another object of the present invention to provide a fork-lift apparatus in a stacker crane where the stable movement of a ram fork regardless of a fall moment is ensured as a counter force on the ram fork is lessened by dispersion.
It is a further object of the present invention to provide a fork-lift apparatus in a stacker crane, a method of controlling the fork-lift apparatus, and a control apparatus for implementing the method.